Q.As a civil engineer, you are given contract to construct a curved road in a ghat. In order to obtain the banking angle θ, you need to decide the speed limit. How will you decide the values of speed v and radius r?
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Start your 14-day free trial to unlock the full solution →r is dictated by the terrain (make it as large as the hillside permits); v is the DESIGN SPEED — a realistic operating speed for the expected traffic — and θ then follows from Eq. (1.2).
The banking formula has two free inputs. RADIUS: in a ghat the road must follow the hill, so r is constrained by the terrain — but every extra metre of radius reduces the needed banking and widens the friction-assisted speed window (Eqs. 1.3–1.4), so the engineer picks the LARGEST radius the alignment allows. SPEED: v is the 'design speed' — not the fastest any vehicle could go, but the realistic speed for the road's expected users: heavy buses and trucks on a climb, sight distances on hairpins, the gradient, and the legal limit for that class of road. Banking exactly at the design speed makes that speed friction-free (safest); vehicles somewhat slower or faster are still served by friction, within the win …
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